In wheelchairs for the elderly or the disabled, movable (raising/lowering) seat bases are used to improve the mobility of their users. From the patent description no. WO0021478 there is known a jack intended for the change of the position of the seat base in wheelchairs, in which a horizontal frame of the seat base comprises a lower and upper part. The lower part is fixed to the wheelchair in a rigid way, and the upper part is movable and moves upwardly and downwardly. The movement of the upper frame is possible due to the operation of the arms of the scissors jack joining both frames. The scissors jack is driven by an electric servomotor, with one end fixed pivotally in a lower frame, and the other end fixed in one pair of arms. When the piston comes out, the upper frame goes up, and when the piston goes back, the return movement takes place. Both frames are permanently parallel to each other, the scope of the movement upwards is regulated by the advance movement of the piston. After the piston goes back, the frames make a compact flat block. On the upper surface of the block there is a proper soft seat base, which is fixed to the upper frame.
From the description of the Polish invention no. P.397089 there is known a scissors jack, in which the drive of the rising scissors mechanism is a servomotor fixed pivotally on a bolt in the lower frame; the other end is fixed pivotally on a bolt in the lever, which is permanently fixed to a pivot fixed pivotally in the lower frame. On the pivot there are permanently fixed cams of the rising system. Cams have some recesses where the bolt can move; the bolt is permanently fixed to a driving arm of the scissors jack. The folded jack has a form of a thin flat block; its fault is a complicated construction of the lever and cam system.